The present invention relates to improvements in making bags, and more particularly to making and filling bags from a continuous sheet of plastic film.
More particularly, the invention relates to an improved method in which completed packets or bags are formed by feeding a thin plastic film over a vertical filling tube to wrap the film around the tube. The edges of the film are joined and the film is pulled downwardly and cross-seals are made at the base of the film. Contents are dropped into the film tubing and a cross-seal is made above the contents and the completed bag is cut from the tubing. An example of this type of mechanism is illustrated in U.S. Pat. No. 4,709,533, Steven Ausnit, as well as in an earlier U.S. Pat. No. 4,617,683, Christoff.
In the formation of bags, the weight or thickness of the film depends upon the type of bag to be formed and the contents thereof. In very thin lightweight film, it is essential that the film is fed uniformly downwardly and this is particularly important where the edges of the film are to be brought together to form a seam along the axial length of the tube. As the thin film is drawn downwardly, it is important that it advance uniformly so that wrinkles are not formed in the film in order that the side seam can be uniformly made. It is also important that the film not be scuffed or torn and a snug wrap of the film around the tube is helpful in making a uniform bag, but this can increase the frictional resistance offered by the outer surface of the tube. This is particularly important in high speed production where the film must be drawn rapidly down over the filling tube and stopped when a cross-seal is made and again quickly pulled downwardly for the next length of film to form the next bag.
In the formation of certain bags, multilayer laminated layer film is used. This film may be composed of different layers of plastic, but frequently includes a layer of metallized film or aluminum foil. This type of film will generate high static charges when fed downwardly over the hollow tube. This has resulted in the necessity of providing a static eliminator, which does not entirely solve the problem. Further, in many cases, the static eliminator is removed or damaged by careless operators. On occasions, complete feed blockage has been experienced with highly charged aluminum foils on days with very low humidity.
It is accordingly an object of the present invention to improve the formation of bags in a form fill process wherein the frictional resistance offered by the filling tube is substantially reduced to insure uniform feed of the plastic film without wrinkling or puckering.
A further object of the invention is to provide an improved form fill machine wherein the plastic film can be formed and drawn more smoothly and evenly than in devices heretofore available.
A still further object of the invention is to provide a new and improved bag-making method in a vertical form, fill machine wherein the generation of static electricity over the feed tube is avoided.